Ordinarily, a container comprises a body, a bottom closing the body at its lower end, and a neck that opens at an upper end of the body to make possible the filling and emptying of the container.
A standard technique for manufacturing containers is blow molding. This technique consists in introducing the blank (i.e., a preform or an intermediate container that has undergone a preforming operation), previously heated to a temperature that is greater than the glass transition temperature of the material (about 80° C. in the case of PET), in a mold provided with a wall that defines a cavity bearing the impression of the container, and in injecting into the blank, through the neck, a fluid, such as a gas (generally air), under pressure to press the material against the wall of the mold.
Under the effect of pressure, the material softened by the heat forms a bubble that inflates and expands both in an axial direction, parallel to the main axis of the mold, and in a radial direction, perpendicular to the axis of the mold.
To prevent any axis deviation of the container and to ensure a good distribution of the material, the axial stretching of the blank is forced by means of a rod that can be moved axially in the mold, this rod comprising a distal end that pushes the bottom of the blank away until it presses it against a mold bottom bearing the impression of the bottom of the container. This technique is called stretch blow molding.
For certain applications, it is known that the mold bottom is movable relative to the wall between an extended position in which the mold bottom is withdrawn relative to the cavity, and a retracted position in which the mold bottom closes the cavity. Initially in withdrawn position, the mold bottom is moved toward its deployed position during the forming of the container.
This technique, called “boxing” and described in detail in the French patent application FR 2 975 332 or its international equivalent WO 2012/156638 (both in the name of Sidel Participations), makes it possible to increase the stretch ratio of the material and has the dual advantage of structurally reinforcing the bottom of the container and of improving the taking of its impression.
The technique of boxing is complex because, depending on the shape and depth of the reliefs (also called reserves) to be made on the bottom of the container, the push-back carried out by the mold bottom can lead to a thinning of the material, even to a local break in the wall of the container in the area of its bottom, which makes it unusable. This is why the adjustment of the manufacturing machines including the boxing function is challenging; it is generally entrusted to experienced operators whose technique makes it possible with judgment to achieve containers that conform. It is then difficult, however, to obtain a consistent quality for the containers, each operator having his own technique. Furthermore, since experienced operators are not always available to correct the adjustments, it is sometimes necessary to stop the production line to avoid the accumulation of containers that do not conform.
During a change in reference (in other words, container model) on the machine, the operator can be led to change certain parameters connected with the boxing, particularly the boxing travel, i.e., the distance separating the retracted position of the mold bottom from its extended position.
Such a modification, if it is not performed correctly, can lead to malformations that affect the containers.
This causes the stopping of the installation, subsequent to the awareness by the operator of a recurring defect affecting the containers manufactured and a scrapping of the containers manufactured between the start of production and the stopping of the installation.
A first objective is therefore to propose a solution that makes it possible to improve the quality of the containers produced.
A second objective is to propose a solution that makes it possible to limit the risks of malformation of the containers, particularly in the area of their bottoms.
A third objective is to limit, indeed prevent, the parameterizing errors during the changes in reference on the installations for manufacturing the containers.